This invention relates generally to modifying the surface properties of percussion tools used in downhole drilling. More particularly, this invention relates to an apparatus, system, and method for reducing friction and/or dispersing heat generated by the sliding motion of a piston within percussion tools, such as rotary bits, shear bits, and hammer bits, used in downhole drilling.
In the drilling industry, percussive hammers have long been used to aid in rock drilling. Historically, a solid piece drill bit and a “down the hole” (“DTH”) hammer have been used as a rock drilling solution. The DTH hammer is a pneumatic tool which is driven by high pressure air. The air drives a piston in a reciprocating motion and when in a downward motion, the piston makes impact onto a mandrel. The piston impacting the mandrel transmits a force into the rock, causing fracture to the rock.
Recently, a rotary and percussion hybrid system (“RPS”) has been investigated for use in the industry. This RPS system also uses a reciprocating piston that is slidably positioned within a casing. This piston is driven by pressurized air. In this system, a roller cone bit, or some other bit type, replaces the solid piece drill bit and the drill mechanically transmits significant downward force and rotation to fracture the rock with a combination of direct load and percussive impact. Like in the DTH hammer, the percussive impact is caused by the piston impacting a mandrel, which transmits a force into the rock.
The piston within the RPS tool, as well as in the DTH hammer tool, slides inside a casing, in a reciprocating manner. Typically, the casing and the piston are both manufactured using steel. During this reciprocating motion, the piston is in contact with at least a portion of the casing and generates friction therebetween. This friction generates heat. Due to the high sliding velocities achieved by the piston, which is about four to five meters per second (m/s) or about sixteen cycles per second, an oil-filled apparatus, otherwise known as an oiler sub (not shown), is typically used to inject oil into the high pressure air stream, which thereby lubricates the piston during operation and reduces the heat generated if compared to when an oiler sub is not used.
The drawings illustrate only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments.